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Tropical Depression Dorian


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If Dorian does end up dissipating over open water or over Hispaniola, it would be doing what about 1 in 4 July-Aug CV storms have done since ~1960...i.e., it is a rather common outcome. It is about as common as a US hit.

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The last run of the hwrf had this going on if you looked at the RH fields and rainfall. The thunderstorms were bursty and lasted for 6 to 18 hours but the surface never responded in deepening the pressure field to concentrate the convection. Its might rain from here to Cuba but the surface winds may never turn west again.

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It appears the remnants of Dorian made a bit of a come back overnight and is now designated 91L. RECON is scheduled to investigate from St Croix later today as well.

 

The GFS shows Dorian regenerating at some point in the 3-5 day range as the remains approach FL. The interesting thing is that the GFS now shows a robust mid-level vortex developing in the next couple of days that has a difficult time bring back a surface reflection. Thats not unlike what the ECMWF has been trying to do the last few days, although it fails to bring the surface circulation back to life.

 

I'm sorta rooting for them to send a recon flight into the remains of Dorian today. ASCAT is nice and works well most of the time, but it still seems to have the most difficulty investigating systems that are producing deep convection (and large cirrus plumes). For example, it had Chantal as an open wave even when there was conclusive evidence that Chantal had a closed circulation per recon. We haven't yet had that benefit with Dorian, and its possible a weak low-level circulation still exist (as there was evidence of that on visible yesterday, despite the ASCAT pass). 

 

We'll see how well the convection can hold together today. While the low-level flow still seems to be a tad faster than the upper-level flow, the low-level ridge has weakened the last 48 hours. The bigger question is if the cirrus plume with Dorian right now is large enough to overcome the TUTT feature located to its west. This upper-level trough has been weakening the last few days, and as long as Ex-Dorian can hold its convective vigor, it could be very interesting to see how these two features interact in the near future. 

 

Latest microwave pass is suggestive... if there is a center is probably around 20N/60.5W

 

20130728.1215.f18.x.colorpct_91h_91v_1de

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Im guessing your thinking andrew but that would be a long shot

That is Fay. I was thinking more on the line of another, but again not suggesting anything. My point is that any disturbance should be carefully watched until its buried and formerly called Dorian should not be writ off yet.  

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The GFS shows Dorian regenerating at some point in the 3-5 day range as the remains approach FL. The interesting thing is that the GFS now shows a robust mid-level vortex developing in the next couple of days that has a difficult time bring back a surface reflection.

 

It finally brings back a surface reflection in of all places, off of Virginia to Massachusetts as it recurves after passing over Southern Florida.

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Not positive that there is a closed circulation, but it's not out of the question. What I do see is a very sharp trough axis extending down to at least Guadaloupe. On satellite, you can see that the low clouds around Guadaloupe are nearly stationary. The winds at Barbuda are interesting as well.

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The GFS shows Dorian regenerating at some point in the 3-5 day range as the remains approach FL. The interesting thing is that the GFS now shows a robust mid-level vortex developing in the next couple of days that has a difficult time bring back a surface reflection. Thats not unlike what the ECMWF has been trying to do the last few days, although it fails to bring the surface circulation back to life.

 

I'm sorta rooting for them to send a recon flight into the remains of Dorian today. ASCAT is nice and works well most of the time, but it still seems to have the most difficulty investigating systems that are producing deep convection (and large cirrus plumes). For example, it had Chantal as an open wave even when there was conclusive evidence that Chantal had a closed circulation per recon. We haven't yet had that benefit with Dorian, and its possible a weak low-level circulation still exist (as there was evidence of that on visible yesterday, despite the ASCAT pass). 

 

We'll see how well the convection can hold together today. While the low-level flow still seems to be a tad faster than the upper-level flow, the low-level ridge has weakened the last 48 hours. The bigger question is if the cirrus plume with Dorian right now is large enough to overcome the TUTT feature located to its west. This upper-level trough has been weakening the last few days, and as long as Ex-Dorian can hold its convective vigor, it could be very interesting to see how these two features interact in the near future. 

 

Latest microwave pass is suggestive... if there is a center is probably around 20N/60.5W

The environment ahead is certainly more unstable than what ex-Dorian has passed through over the past several days. Really, conditions in the Bahamas are actually not so bad aside from the TUTT, which based upon latest satellite data may weaken a bit faster than what the GFS shows. Because ex-Dorian is generating so much convection, it is already starting to redevelop a (rather robust?) MLC almost exactly where you mention a possible LLC. This could mean that ex-Dorian, if it regenerates, may be a bit stronger than what the dynamical models show within the next four days. After all, the LGEM and DSHP have been consistently forecasting a 50- or 60-kt TS sometime within this time frame. I am not saying that it will happen, but I could easily see a scenario in which some models bust re: low prospects of regeneration. Because ex-Dorian has remained weak in the short term, this should allow a track N of Hispaniola and through the Bahamas and into SE FL, which is certainly different from my expectations of dissipation over Hispaniola. Now I am willing to countenance a regeneration.

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Not positive that there is a closed circulation, but it's not out of the question. What I do see is a very sharp trough axis extending down to at least Guadaloupe. On satellite, you can see that the low clouds around Guadaloupe are nearly stationary. The winds at Barbuda are interesting as well.

 

If you look at the low clouds under the cirrus shield further N, I suppose they could reflect 10 knot or so SW winds.

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The GFS shows Dorian regenerating at some point in the 3-5 day range as the remains approach FL. The interesting thing is that the GFS now shows a robust mid-level vortex developing in the next couple of days that has a difficult time bring back a surface reflection. Thats not unlike what the ECMWF has been trying to do the last few days, although it fails to bring the surface circulation back to life.

Perhaps the 12Z GFS does not show as much of a mid-level circulation due to the influx of some drier mid-level air from the NE. The low-level ridge shifts W over the next two days and may continue to allow some SAL into the N side of the system. Is that why convection is still pulsating at this time? If so, then the mid-level dry air would prevent shear from being less due to less convection (= less outflow).

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A TROUGH OF LOW PRESSURE...ASSOCIATED WITH THE REMNANTS OF DORIAN...
IS PRODUCING AN AREA OF SHOWERS AND THUNDERSTORMS...AS WELL AS
WINDS TO GALE FORCE...A FEW HUNDRED MILES NORTH AND NORTHEAST OF
THE LEEWARD ISLANDS. AN AIR FORCE RECONNAISSANCE AIRCRAFT IS
CURRENTLY INVESTIGATING THE SYSTEM TO DETERMINE IF A CLOSED
LOW-LEVEL CIRCULATION AND A WELL-DEFINED CENTER HAVE REDEVELOPED.
ENVIRONMENTAL CONDITIONS ARE MARGINALLY CONDUCIVE FOR
REGENERATION...BUT ONLY A SMALL INCREASE IN ORGANIZATION COULD LEAD
TO THE REFORMATION OF A TROPICAL CYCLONE. THIS SYSTEM HAS A MEDIUM
CHANCE...30 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE
NEXT 48 HOURS AS IT MOVES WESTWARD TO WEST-NORTHWESTWARD AT 15 TO
20 MPH...PASSING NORTH OF THE LEEWARD ISLANDS AND PUERTO RICO TODAY
AND MONDAY...AND MOVING OVER THE TURKS AND CAICOS ISLANDS AND
SOUTHERN BAHAMAS ON TUESDAY.

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Strongly worded TWO for only 30%

 

A TROUGH OF LOW PRESSURE...ASSOCIATED WITH THE REMNANTS OF DORIAN...
IS PRODUCING AN AREA OF SHOWERS AND THUNDERSTORMS...AS WELL AS
WINDS TO GALE FORCE
...A FEW HUNDRED MILES NORTH AND NORTHEAST OF
THE LEEWARD ISLANDS. AN AIR FORCE RECONNAISSANCE AIRCRAFT IS
CURRENTLY INVESTIGATING THE SYSTEM TO DETERMINE IF A CLOSED
LOW-LEVEL CIRCULATION AND A WELL-DEFINED CENTER HAVE REDEVELOPED.
ENVIRONMENTAL CONDITIONS ARE MARGINALLY CONDUCIVE FOR
REGENERATION...BUT ONLY A SMALL INCREASE IN ORGANIZATION COULD LEAD
TO THE REFORMATION OF A TROPICAL CYCLONE
. THIS SYSTEM HAS A MEDIUM
CHANCE...30 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE
NEXT 48 HOURS AS IT MOVES WESTWARD TO WEST-NORTHWESTWARD AT 15 TO
20 MPH...PASSING NORTH OF THE LEEWARD ISLANDS AND PUERTO RICO TODAY
AND MONDAY...AND MOVING OVER THE TURKS AND CAICOS ISLANDS AND
SOUTHERN BAHAMAS ON TUESDAY.

 

 

12z HWRF and GFDL do virtually nothing with 91L/xDorian 

 

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